Crankshaft wear?

2 replies to this topic
  • tnl

Posted December 05, 2007 - 12:58 PM


Bike's in the shop right now to have the case replaced and the Tech. (not from a Yamaha dealer but reputable) looked over some other components and suggest replacing the following parts: my crankshaft assembly because of some signs of wear and tear, cylinder has straight, vertical scratches in it but I can't feel them with my fingernail (but visible) and I don't notice any lack of power and doesn't blow any smoke, primary drive gear showing signs of wear. Bike is a 05 450 with 70 hours on it, oil change every 5 hrs, air filter cleaned every ride, synthetic oil (Valvoline mx4t), Scott's oil filter, never been raced/rec. rider. Is it abnormal to need to replace these items when the case is split opened even if it's in spec? I need to find out exactly what wear and tear they are referring to I guess? Tough question I guess but just wanted some input on how far to go with these additional parts about $700 worth? If the wear and tear is in spec then I think I should leave it but I think the parts inside the case are tougher to replace later. I also don't want anything to fail if I opt to not have them replaced now. Kinda like $700 now or $2500 later. I hear alot about people getting alot more hours out of their bikes before replacing all this stuff. Am I doing something wrong? A money decision I guess?

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  • grayracer513

Posted December 05, 2007 - 02:13 PM


The only reason you would replace the crank is if the cam drive sprocket is seriously worn, or the rod is loose. See page 2-7 of your manual for how to check this, and be sure that when you check the play by rocking the rod (F), you don't confuse the rocking with side clearance (A). With any bearing that has time on it, the thing you can't know is when or whether it will fail from fatigue. That's where the guessing comes in. There's no sound reason not to swap out the main bearings, though.

The test on the cylinder is simple: make 4 passes at it with a spring-ball hone. If the scratches are still visible, consider replacement. If not, replace the rings and be on your merry way.

  • 642MX

Posted December 05, 2007 - 05:10 PM


If it was mine, I'd go ahead and replace the main bearings and the big end bearing. Reading about seized cranks on 4xx's are not real common, but when they break they tend to cost a small fortune to fix.

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